Mitox coughing and spluttering

[russtobin]

Got a Mitox 281 MT that after about 10-15 minutes use won't rev beyond idle without stalling.

Machine is only a couple of years old and has been used lightly.

Anyone got any ideas as to likely cause?

Many thanks in advance for any replies.

[spudulike]

Got a Mitox 281 MT that after about 10-15 minutes use won't rev beyond idle without stalling.

Machine is only a couple of years old and has been used lightly.

Anyone got any ideas as to likely cause?

Many thanks in advance for any replies.

 

Sounds like fuel starvation at high speed although it may have had a partial seize at some stage.

 

Worth pulling the exhaust off and looking at the piston through the exhaust port, it should be smooth and grey with no black vertical scores.

 

If that is ok then check the gauze strainer filter inside the carb, it may be filled with fine wood chip!

[russtobin]

Piston seems to be aok with no score marks and is metallic in colour.

Spark plug is really black and oily though!

Running 40:1 fuel mix.

A bit wary about stripping the carb just yet - also the problem only occurs once the machine has been running for awhile. It revs aok once started.

[spudulike]

Piston seems to be aok with no score marks and is metallic in colour.

Spark plug is really black and oily though!

Running 40:1 fuel mix.

A bit wary about stripping the carb just yet - also the problem only occurs once the machine has been running for awhile. It revs aok once started.

 

If it has a black plug then it sounds like it is running mega rich. It may be good time to see if the H screw needs adjustment or it is possible either the air filter is blocked or the choke flap isn't fully opening when the choke is taken off.

 

Just be aware that if you lean off the H screw too much, it can seize the engine!

[russtobin]

Thx for that.

Yeah I suspect it's the mixture that needs sorting.

I'll have to invest in an adjustment tool as the carb on my machine has only one D shaped adjuster.

I'll also take heed and make very small adjustments.

Anyone know which way to turn the adjuster to lean things up?

[spudulike]

Thx for that.

Yeah I suspect it's the mixture that needs sorting.

I'll have to invest in an adjustment tool as the carb on my machine has only one D shaped adjuster.

I'll also take heed and make very small adjustments.

Anyone know which way to turn the adjuster to lean things up?

 

Clockwise, Gardenkit may know the standard setting, generally one turn out from fully in but don't assume this.

[russtobin]

Managed to get thru to someone at Mitox UK and they reckon turn the adjuster "until the engine revs its nuts off" then back off by qtr turn.

Because mine is running super rich think I'll need to turn anticlockwise to get it to rev - turning clockwise will probably stall the engine. Will know more once I get the adjustment tool.

Mitox advise that 40:1 fuel mix means engine seizure unlikely......

[GardenKit]

I would have thought that if its running 'super rich' then you will need to turn it clockwise to lean it up. We are talking about the high speed screw here, so its unlikely to stall whichever way you turn it.

So with it started, turn it in a little and see if the engine picks up , then when its reving keep turning in until the revs peak, then out (anticlockwise) until the revs start to drop off and a little fourstroking can be heard, the turn very gently in (clockwise) until the fourstroking just disappears. Make sure you have full length of 2,4 cord in the head before you try this, as that is the required 'load'

 

It could be that your low speed (idle) mix needs tweaking too, to get a pickup from idle.

 

By the way, it might be better to run it on 50:1 of a good quality semi synthetic to avoid the oily plug issues.

[Stubby]

In is lean out is rich irispective of left or right thread ..if that helps .

[russtobin]

Thx for all that.

There seems to be only one adjustable screw which doesn't have an obvious screw head only a small V cut into its side.

Does this sound right??